I was in a lunatic asylum once but it wasn't very exciting.

I'm using the term 'lunatic asylum' on purpose. That antiquated phrase dredges up images which persist when we talk about mental health. There are still whisperings and tongue clucks of sympathy when someone we know a friend endures a mental illness. There's no shame in incurring a broken ankle because you fell, or having flu because someone sneezed beside you on the train, so why should there be shame if you develop anxiety following a period of stress, or depression following a bereavement?

Every action has a reaction. Circumstances create broken bones and wheezy lungs just as they create bleak depressions and panic attacks.

Yet, outdated concepts of madness and the loony bin are still here and they're still terrifying. If you think of being treated for a broken leg you might imagine a clumsy stookie and your pals crowding in to sign it, but if you think of being treated for a mental disorder you might imagine padded cells, electric shocks, locks, straps and shaven heads, and your friends can't draw funny faces on a strait-jacket.

So when I entered a 'lunatic asylum' - as a grape-clutching visitor, you understand - I was surprised at how normal it seemed. The ghoul in me was even disappointed. Had I expected bolts and howls and rattling bars? There was nothing of the sort. Instead of bolts there were little blinking keypads set into the wall, the type you find in every office. Instead of stony corridors there was bright linoleum and smooth, mint-green wallpaper. There were magazines and armchairs and leaflets. It just looked like every other hospital.

Paul Whitehouse's new comedy, Nurse (BBC2), is about a Community Mental Health Nurse who visits her patients in their homes. It was noticeable that almost all of the patients lived in drab, dingy rooms, with dusty light struggling through the net curtains. Why the squalor? Is it because 'loonies' can't look after themselves? No, I think Nurse was drawing attention specifically to the state of community nursing.

If a mental health patient is hospitalised they'll be cared for in a shiny hospital, in bright white wards, surrounded by beeps and bleeps and squeaky floors. But what happens when the patient is sent home? According to Nurse, and countless media stories, help often falls away. If you're lucky you might be nudged onto a waiting list for a therapist but that list will be as long as a biblical scroll and you may well drop off the radar. The lucky ones will have a nurse visit them at home (or perhaps they're the unlucky ones as they're the people in direst need) but the harassed Community Nurse will have a list of patients as long as that waiting list scroll. But she'll do her best, driving from house to house, visiting people in the tired, neglected places they've been relegated to once the mighty white hospital discharges them.

Liz is the good-hearted Nurse doing her rounds without complaint or exasperation. She is probably the ideal nurse of the popular imagination, being kind and motherly but also gently strict when required. In the course of the 30 minute episode she attends a huge assortment of patients - most of whom are brilliantly played by Paul Whitehouse - leaving you sure the programme was twice as long, because so much suffering and wit has been crammed in.

And just as we have one view of a mental hospital, we have two of a person suffering mental illness. They'll either be depressed or anxious. Nurse shows a variety of mental illnesses, prodding us to remember how vast the field is, and how badly it needs more discussion and more resources. It even covers conditions which don't seem to immediately qualify as a mental illness, such as Graham's.

Graham is morbidly obese and, according to some right-wing commentators, that's not an illness, it's just a case of too many chips. Liz makes it clear that Graham is severely depressed and overeats as comfort. 'Exercise is a very useful took for combating depression,' she says and this very matter-of-fact line, consisting of common sense and medical opinion, summarises what this comedy is about. There are laughs, yes, with Graham and his tetchy old mum squabbling and bitching at one another, but the comedy runs alongside real mental illness and true representations of how it's treated.

The illnesses are monstrously magnified for comic effect. There's a lady with severe depression who lives in a filthy house with stinking cats, and whose only contact with the outside world is a neighbour who takes her on trips to the crematorium. There's a has-been popstar who boasts breathlessly, 'I was the first person in the county of Hampshire to wear a satin jacket!' but he has to eventually hitch up his kimono, lean over his gold painted harp and accept an injection in the buttocks. Interestingly, the manic pop star was the only patient who lived in a bright house.

So Nurse is a perfect blend of comedy and common sense. The ragtag assortment of patients provide the comedy, presenting their illnesses in exaggerated form, and Liz is the thread of common sense which joins the patients together. Without Liz this would be a sketch show. With Liz it's a hugely compassionate comedy.